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A TENNESSEE COTTON field, pictured in early July 2011, is overgrown with resistant pigweeds. Stuck with a bad situation, the producer tilled the field up and replanted.

The continuing spread, consequences and best ways to manage herbicide-resistant weeds were again key talking points of speakers at the annual Tri-State Soybean Forum. And hand-in-hand with such weeds is the need to protect herbicides that still work.

The point was driven home during the presentation of Larry Steckel, University of Tennessee weed specialist.

“We did a survey in Tennessee last year and 60 percent of our Liberty Link soybeans got nothing but Liberty on them,” during the Jan. 3 meeting in Dumas, Ark. University of Arkansas weed scientist Jason Norsworthy “ran a similar survey here in Arkansas and found similar results. Folks, we’re going to run Liberty into the ground if that’s the case. We’ve got to use other modes of action if we’re going to protect it and keep it around for any length of time.

“We’ve got to control (resistant pigweeds) early and up-front and overlay residuals as best we can.”

Steckel showed the audience a photo of a cotton field overgrown with pigweeds. “I’m sure a lot of you are very familiar with this type of situation. This is one of the many fields I was called to back in 2011. That was our high-tide for Palmer pigweed – the worst year, by far.

“I was called to this field on June 21, 2011. The farmer was about 24 hours too late spraying his Flexstar. If he’d been 24 hours earlier, he’d probably been pretty good.”

That night, about 8:00, Steckel scrolled through his phone log and found some 80 missed calls. “Almost all of them were about fields that looked like this. Most of (the callers) were retailers and county Extension agents talking about multiple problem fields. That was the first year that it dawned on me just how serious a problem this was.”

There’s no good answer in such situations, said Steckel. The farmer elected to till the field up and replant.

A photo taken on August 1 showed a cleaner field. “He used a residual the second time. The pigweed you see aren’t new germinators. Those re-rooted. You must be very aggressive with tillage on big pigweeds to affect them.

“Of course, another option is to try and keep beating at the weeds with herbicides. But that’s throwing good money after bad. So, you’ve got to take care of the problem up front the best you can with pre-emergence herbicides and overlaying residuals.”

Tennessee producers have handled pigweeds much better since 2011. “In 2012 and 2013 I’ve been pretty proud of where we are compared to where we were. It isn’t coming cheap, though, and it’s not coming easy.

“Typically, we go out with Roundup, dicamba and some kind of residual. Right behind the planter we spray gramoxone because you don’t dare leave a pigweed up and you want to take out any strangler marestail that got past the burndown.

“Then, we use a residual. I don’t have a big pick of the litter to use, although I like a herbicide with at least two effective sites of action for Palmer pigweed in the mix. We have the Valor-based products, Dual-based products, pyroxasulfone-based products, and even the Authority-based products. All would be good foundations, maybe get some metrabuzin in the mix.

“Then, try to overlay another residual over the top of the soybeans -- a Dual, a Prefix. One I like best post-emergence is Prefix.”